Structurally variable stents

ABSTRACT

The stent has at least two different patterns along its longitudinal length such as a closed cell and an open cell design. The stent is made from nickel/titanium, titanium, stainless steel or a noble metal. The different patterns are joined by varying articulations including a W-pattern and S-patten. The stent has at least two coatings over the base structure, the coating depth not exceeding ten microns.

BACKGROUND OF THE INVENTION

[0001] This invention relates to stents used to support aterial andvenous conduits in the human body. More particularly, it refers to atubular stent having a non-uniform structure along its longitudinallength to provide good flexibility and radial strength.

[0002] There are four major classes of stents employed in the prior art.These four major classes of stents are described as follows:

[0003] 1. Coil Stents are made from a single wire. The wire is bent invarious ways and formed into a stent. Examples of this type of stent arethose shown in U.S. Pat. Nos. 4,969,458; 4,681,110 and 5,824,056.

[0004] 2. Slotted Tube Stents are laser cut using a tube of eitherstainless steel, nickel/titanium alloy (NITINOL®), titanium or any othersuitable materials. These designs are preprogrammed into a machinelanguage and a laser is used to cut the programs. These stents have auniform design and a uniform thickness from the beginning to the end ofthe stent. In other words, the same segment is repeated from one end ofthe stent to the other. Examples of this type of stent are described inU.S. Pat. Nos. 4,733,665; 4,739,762; 4,776,337 and 4,793,348.

[0005] 3. Self Expanding Stents are usually braided or knitted withmultiple wire filaments such that they have a lower profile whenstretched and they expand from a lower profile to a higher profile whenunconstrained in the body. These stents are called self-expanding stentsand are described in U.S. Pat. No. 4,655,771.

[0006] 4. Hybrid Stents are similar to slotted tube stents except thatthey do not have a closed cell structure but have an open cellularstructure with flexible interconnections between each segment of thedesign. These interconnections provide the flexibility while thesegments provide the radial strength and other important properties ofthe stent. Examples of this stent are described in U.S. Pat. Nos.5,514,154; 5,562,728; 5,649,952 and 5,725,572.

[0007] In use, each of the four classes of stents described above arecoated as described in various patents as follows:

[0008] 1. U.S. Pat. No. 5,759,174, describes a balloon that has aradiopaque segment attached to one of the longitudinal ends of theballoon. When the balloon is inflated, the stent is pressed against theends of the artery and this indicates the center portion of the dilatedstenosis. The external radiopaque marker band is typically made from adense radiopaque metal such as tantalum, gold, platinum or an alloy ofthose dense metals.

[0009] 2. U.S. Pat. No. 5,725,572, describes gold plating on the ends ofa stent such that the gold plating marks two bands at the ends of astent. The patentee mentions that the limitation of gold coating is thestiffening of the stent surface. Hence, the gold plating is done only atthe ends where the stiffening does not significantly alter theproperties of the stent. Also described is another embodiment where onlythe exterior of the stent is coated with a radiopaque material.

[0010] 3. U.S. Pat. No. 5,919,126, describes a patent where the body ofthe stent is formed from a non-radioactive structural material, aradiopaque material coats the body and a beta emitting radioisotope ionis implanted into the radiopaque material.

[0011] 4. U.S. Pat. No. 5,824,056 describes an implantable medicaldevice formed from a drawn refractory metal having an improvedbiocompatible surface. The method by which the device is made includescoating a refractory metal article with platinum by a physical vapordeposition process and subjecting the coated article to drawing in adiamond die. The drawn article can be incorporated into an implantedmedical device without removing the deposited material.

[0012] 5. U.S. Pat. No. 5,824,077 describes a stent which is formed ofmultiple filaments arranged in two sets of oppositely directed helicalwindings interwoven with each other in a braided configuration. Each ofthe filaments is a composite including a central core and a casesurrounding the core. The core is formed of a radiopaque material whilethe outer casing is made of a relatively resilient material, e.g., acobalt, chromium based alloy. Alternative composite filaments describedin the patent employ an intermediate barrier layer between the case andthe core, a biocompatible cover layer surrounding the case, and aradiopaque case surrounding the central core.

[0013] 6. U.S. Pat. No. 5,871,437 describes a non-radioactive metallicstent which is coated with a biodegradable or non-biodegradable thincoating of less than about 100 microns in thickness which is selected toavoid provoking any foreign body reaction. This coating contains aradioactive source emitting Beta particles with an activity level ofapproximately one micro curie and on top of this layer is ananticoagulant substance to inhibit early thrombus formation.

[0014] 7. U.S. Pat. No. 6,099,561 describes a stent having abiocompatible metal hollow tube constituting a base layer having amultiplicity of openings through an open ended tubular wall thereof, thetube constituting a single member from which the entire stent isfabricated. A thin tightly adherent intermediate layer of noble metaloverlies the entire exposed surface area of the tube including edges ofthe openings as well as exterior and interior surfaces and ends of thewall. A third outermost ceramic like layer composed of an oxide,hydroxide or nitrate of a noble metal is formed atop and in adherentrelation to an intermediate layer.

[0015] 8. U.S. Pat. No. 5,722,984 describes a stent which has anantithrombogenic property and contains an embedded radioisotope thatmakes the coating material radioactive.

[0016] 9. Other relevant patents that describe the coating technology orcoating properties include U.S. Pat. Nos. 5,818,893; 5,980,974;5,700,286; 5,858,468; 5,650,202 and U.S. Pat. No. 5,696,714.

[0017] Although some of the above mentioned stents have good flexibilityand others have good radial strength, there is no optimum stent in theprior art that has both good flexibility and radial strength togetherwith the ability to retain a useful coating.

SUMMARY OF THE INVENTION

[0018] The present invention describes a fifth class of stents havingmultiple designs of structurally variable configuration along thelongitudinal length of the stent. The stent has one pattern at both endsof the stent to provide optimal flexibility and a different pattern atthe mid-portion of the stent to provide optimal radial strength.Alternatively, the stent has one pattern at each end, a differentpattern at its mid-portion and a third pattern in-between themid-portion and each end. The stent has both closed cell and open cellconfiguration along its longitudinal length and the closed cells andopen cells are interlinked with either straight or wavy configurationsin a single stent.

[0019] A preferred pattern contains at least three differentconfigurations selected from an open cell design, a closed cell design,a straight interlink or articulation and one wavy interlink orarticulation along a variable thickness of connecting stents. Because ofthe variable thickness of the stents, the amount of drug loaded on thestent is varied along with the release characteristics.

[0020] The structurally variable stents of this invention usually have astainless steel or nickel/titanium alloy (NITINOL®) base material withtwo layers of coating together not exceeding ten microns in depth. Onelayer is an undercoat in direct contact with the base metal both on theinside and outside surface of the base metal. The topmost layer is incontact with the blood. Both the undercoat and top coat are of the samematerial such as metallic, biological, synthetic material, or polymericmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention can be best understood by those having ordinaryskill in the art by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which:

[0022]FIG. 1 shows a closed cell design of a stent.

[0023]FIG. 2 shows a closed cell design of a stent interconnected by astraight bridge.

[0024]FIG. 3 shows an exterior design of a closed cell stent.

[0025]FIG. 4 shows a design of an open cell stent with a radiopaquecoating on one section of the stent.

[0026]FIG. 5 shows a design of a coil stent.

[0027]FIG. 6 shows a design of a structurally variable stent having anopen cell design on the ends and a closed cell design at the center ofthe stent.

[0028]FIG. 7 shows a design of a structurally variable stent withvariable thickness of the open and closed cell design.

[0029]FIG. 8 shows a design of a structurally variable stent with opencell at the ends and closed cell at the mid-portion and alternatingarticulations between both the open and closed cell.

[0030]FIG. 9 shows a design of a structurally variable stent with bothopen and closed cell design and the articulations at the end of theclosed cell design is an S-shape rather than a W-shape.

[0031]FIG. 10 shows a design of a structurally variable stent with bothopen and closed cell design and alternating articulations at varioussections of the stent.

[0032]FIG. 11 shows a design of a structurally variable stent with anopen cell design at the ends with multiple S-shapes and a straightarticulating member and closed cell design and the mid-portion with acomplex plus sign articulation.

[0033]FIG. 12 shows a design of a structurally variable stent with acircle at a mid-portion of the open cell design.

[0034]FIG. 13 shows a design of a structurally variable stent withdifferent wall thickness along the length of the stent.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Throughout the following detailed description the same referencenumerals refer to the same elements in all figures.

[0036] Referring to FIG. 1, the closed cell tubular stent design 10 hasa longitudinal series of cells 12. As seen in FIG. 2, the cells 12 areinterconnected by a bridge 14. The exterior look of such a stent 10 isseen in FIG. 3. In contrast, FIG. 4 shows the design of an open cellstent 16 having multiple open cells 18. One section 20 of the open cellstent 16 has a radiopaque coating 22.

[0037] A coil stent 24 design is shown in FIG. 5.

[0038] Referring to FIG. 6, the stent 26 of this invention is shown. Thestent 26 has an open cell 16 configuration at each end and a closed celldesign 10 at the center portion of the stent 26. Connecting struts 28join the components.

[0039] The stent 26A shown in FIG. 7 has the same configuration as stent26 shown in FIG. 6, except that the thickness of the structure varies.The articulations 30 in a W-pattern are all the same. In FIG. 8, incontrast, articulations 32 are in the shape of an S-pattern while otherarticulations 30 remain in the W-pattern.

[0040] In FIG. 9, the stent 26B has a closed cell design 10 at itsmid-portion and an open cell design 16 at each end. The articulations 32are all in the shape of an S-pattern. In FIG. 10, the stent 26C has aclosed cell design 10 at its mid-portion and an open cell design 16 ateach end, but with alternating S-pattern 32 and W-pattern 30articulations.

[0041] In FIG. 11, the stent 26D has an open cell design 16 at its endsin an S-pattern, a straight articulating member 34, a closed cell 10mid-portion with a complex plus sign pattern articulation 36.

[0042] In FIG. 12, the stent 26E has an open cell design 16 at its endswith a circle 38 in the open cell design. The center portion is a closedcell design 10.

[0043] In FIG. 13, the stent 26F has thick 40 and thin 42 wallthickness.

[0044] The combination of an open cell 16 and closed cell 10 stentdesign creates a stent having both flexibility and radial strength alongthe length of the stent. The variable stent thickness 40 and 42 providesgreater functional properties for coating the stent. If the coating isto enhance the radio opacity, then the ends can be made more radiopaquethan the mid-portion. If the objective of a coating is to load moredrugs then the ends of the stent can be thicker to allow for suchcoating. Since restinosis occurs in a stent invariably at its ends, ahigher drug concentration at the ends can more thoroughly inhibit suchrestinosis.

[0045] The thickness of the open cell design 16 versus the closed celldesign 10 may vary as seen in the drawings. The open cell design 16 isgenerally twenty-five percent thicker than the mid-portion or closedcell design 10.

[0046] It is preferred to have two layers of coatings on the entirelength of the stent 26. A base coat of metal and a top coat of metalenhances radio opacity of the stent 26. A base coat of a polymericcoating has a top coat of a drug which slowly diffuses out of the stent26 over a period of time. The variable design stents 26-26F of thisinvention allows the loading of drugs at the ends to facilitate a gradedrelease profile.

[0047] The stents 26-26F of this invention are longitudinal,cylindrical, metal structures having at least an open cell and closedcell design joined together by struts. The metal can be nickel-titaniumalloy (NITINOL®) titanium, stainless steel or a noble base metal. Acoating of at least two layers over the base metal has a depth not toexceed ten microns.

[0048] Typical coatings are set forth in U.S. Pat. Nos. 5,759,174;5,725,572; 5,824,056; and 5,871,437 and are herein incorporated byreference.

[0049] The above description has described specific structural detailsembodying the variable stents of this invention. However, it will bewithin the skill of one having ordinary skill in the art to makemodifications without departing from the spirit and scope of theunderlying inventive concept of these structurally variable stents.

Having thus described the invention in detail the following is claimed:1. A tubular stent for supporting aterial and venous conduits in thehuman body, the tubular stent comprising: a longitudinal cylindricalmetal base structure having at least two different patterns along itslongitudinal length, the patterns joined by struts having apredetermined articulation, the base structure coated by at least twolayers having a depth not exceeding ten microns.
 2. The stent accordingto claim 1 wherein one pattern is a closed cell design and a secondpattern is an open cell design.
 3. The stent according to claim 1wherein one pattern is a closed cell design and a second pattern is aslotted tube design.
 4. The stent according to claim 1 wherein onepattern is a closed cell design and a second pattern is a coil design.5. The stent according to claim 1 wherein one pattern is an open celldesign and a second pattern is a slotted tube design.
 6. The stentaccording to claim 1 wherein one pattern is an open cell design and asecond pattern is a coil design.
 7. The stent according to claim 1wherein one pattern is a slotted tube design and a second pattern is acoil design.
 8. A tubular stent for supporting aterial and venousconduits in the human body, the tubular stent comprising: a longitudinalmetal base structure having a multiplicity of different circumferentialmembers interconnected by articulations of varying configuration, thebase structure coated by at least two layers having a depth notexceeding ten microns.
 9. The stent according to claim 8 wherein opencell and closed cell members are the different circumferential members.10. The stent according to claim 9 wherein the open cell member isconnected to the closed cell member with a W-articulation.
 11. The stentaccording to claim 9 wherein the open cell member is connected to theclosed cell member with an S-articulation.
 12. The stent according toclaim 8 wherein the different circumferential members vary in base metalthickness.
 13. The stent according to claim 8 wherein the coatings areof a radiopaque substance.
 14. The stent according to claim 8 whereinthe coatings are of a biological substance.
 15. The stent according toclaim 8 wherein the coatings are polymeric.
 16. A tubular stent forsupporting aterial and venous conduits in the human body, the tubularstent comprising: a longitudinal cylindrical metal base structure havinga single pattern at each end along the longitudinal cylindrical metalbase structure and a different pattern at a mid-portion of the basestructure, each pattern joined by an articulation of varyingconfiguration, the patterns coated with at least two layers of abiological substance.
 17. The stent according to claim 16 wherein thesingle pattern at each end of the base structure has a thicker layer ofbiological substance than the mid-portion.
 18. The stent according toclaim 16 wherein the end pattern at each end of the base structure is anopen cell design and the mid-portion of the base structure is a closedcell design.
 19. The stent according to claim 18 wherein the closed celland open cell pattern is connected by an S-articulation.
 20. The stentaccording to claim 18 wherein the closed cell and open cell pattern isconnected by a W-articulation.
 21. The stent according to claim 18wherein the open cell pattern at each end has multiple S-shapes and astraight articulating member, the closed cell pattern connected to theopen cell pattern with a complex plus sign articulation.
 22. The stentaccording to claim 18 wherein the open cell pattern at each end has acircle at a mid-portion of the open cell pattern.